avutil/imgutils: always zero data pointers in av_image_fill_pointers()

This restores the relevant behavior of the function as it was before
3a8e927176.

Signed-off-by: James Almer <jamrial@gmail.com>

libavutil/imgutils.c

@@ -150,6 +150,8 @@ int av_image_fill_pointers(uint8_t *data[4], enum AVPixelFormat pix_fmt, int hei
     ptrdiff_t linesizes1[4];
     size_t sizes[4];
 
+    memset(data     , 0, sizeof(data[0])*4);
+
     for (i = 0; i < 4; i++)
         linesizes1[i] = linesizes[i];
 
@@ -164,8 +166,6 @@ int av_image_fill_pointers(uint8_t *data[4], enum AVPixelFormat pix_fmt, int hei
         ret += sizes[i];
     }
 
-    memset(data , 0, sizeof(data[0])*4);
-
     data[0] = ptr;
     for (i = 1; i < 4 && sizes[i]; i++)
         data[i] = data[i - 1] + sizes[i - 1];